This invention is an improvement over U.S. patent application Ser. No. 407,121 now U.S. Pat. No. 3,924,824, Oct. 10, 1973, assigned to the same assignee as the present invention.
A strapped down navigation system derives its name because the inertial components comprising the gyros and accelerometers are "strapped down" or body mounted to the vehicle in which it is contained. In conventional strapped down inertial navigation systems, the gyro torquers are driven to force the spin axis (also referred to as the momentum vector) to coincide with the null axis. This practice necessitates a high up-date rate in the computer on the integration of the attitude equation. It also requires that the maximum torquer rate be able to compensate for high frequency small angle body motions. Basic to the disclosure of the application referred to above is a concept of a two step transformation from body fixed to inertially fixed coordinate frames. The first of these transformations is an attitude transformation based upon gyro pickoff outputs. The second transformation is based upon the angular rate of the gyro's momentum vector. This concept remains unchanged in the present invention and the improvements of the present invention include the above cross-track navigation concept and extends it to general all axis, all attitude navigation. Moreover, the present invention overcomes the restriction of the above device that the trajectory of the vehicle must be close to planar.